1. FIELD OF THE INVENTION
This invention relates to a magnetic head formed of two half cores connected to each other.
2. PRIOR ART
The coercive force of magnetic recording medium has been improved because of the increasing need for high-density magnetic recording. Correspondingly, development is being promoted of a magnetic head which can be adapted to perform recording on such a magnetic recording medium and which is formed, at least at portions facing a magnetic gap, from a magnetic material which enables a high degree of saturation magnetic flux density.
The inventors of the present invention also studied this type of magnetic head from various aspects and proposed a magnetic head which is formed by using a core half body which is constituted by use bases having side surfaces formed on the side of a magnetic gap and inclined relative to the magnetic gap surface, and thin magnetic films that are made of a magnetic material enabling a high degree of magnetic flux density and that cover the side surfaces of the core bases on the side of the magnetic gap (Japanese Patent Unexamined Publication No. 155513/1983).
Other types of heads designed to improve the wear resistance of head cores and reduce sliding noise have been proposed. For example, a head in which core base portions in the recording medium sliding surface are formed from a non-magnetic material (Japanese Patent Unexamined Publication No. 116809/1978) and a head in which a portion between the front surface and a winding window is formed from a non-magnetic material and in which a back core is formed of high-permeability cores (Japanese Patent Unexamined Publication No. 184705/1986) are known.
FIG. 15 shows a perspective view of the above-described type of magnetic head having non-magnetic bases 1a and 1b, magnetic layers 2a and 2b formed from a high permeability magnetic material, glass 3, a head gap 4, and a winding window 5.
A method of producing this magnetic head will be described below with reference to FIGS. 16 to 22.
Referring to FIG. 16, a pair of grooves 14 are formed in one surface of a ferrite block 1 from which the core half body 1a or 1b is formed. The grooves 14 are formed in such a manner that they are parallel with and close each other. A thread of a projection 15 having an acute tip (apex) is formed in each groove 14. Next, a thin magnetic film 2 made of a high-permeability magnetic material capable of enabling a high degree of saturation magnetic flux density is formed uniformly by a thin film forming technique such as vapor deposition or sputtering on the surface in which the grooves 14 and projections 15 are formed (refer to FIG. 17).
As shown in FIG. 18, a reinforcement layer 16 made of a non-magnetic material such as glass is formed on the thin magnetic film 2 with a comparatively substantial thickness, and these members are polished to a level indicated by the chain line in FIG. 18. FIGS. 19 and 20 show a resultant structure in which the thin magnetic film 2 is partially removed by polishing above the tips of the projections 15 so that it has flat portions 17.
The block thus formed is partially cut to a predetermined depth so as to form a coil groove 18 which extends in the direction perpendicular to the threads of projections 15, as shown in FIG. 21, thereby obtaining a core half body 1a. The core half body 1a in which the coil groove 18 is formed and a block having no coil groove 18 (Refer to FIG. 20; this block serves as the core half body 1b.) are integrally connected to each other by glass bonding so that glass portions 5 face each other, as shown in FIG. 22. The blocks thus connected are sliced along planes indicated by the chain lines in FIG. 22, thereby obtaining a magnetic head such as that shown in FIG. 15.
However, in the above-described type of magnetic head, a large amount of glass is used to connect the two core half bodies and, therefore, in the process of setting and cooling the glass after melting, a large degree of residual thermal stress occurs in the glass 3 due to the very small difference between the thermal expansion rates of the magnetic layers 2a and 2b of a high saturation magnetic flux density and the glass 3. This stress can cause the magnetic layers 2a and 2b to come off and the glass 3 to be cracked, resulting in a considerable lowering of the productivity of the magnetic head manufacturing process.
In addition, the glass 3 tends to wear at a higher rate compared with the non-magnetic bases 1a and 1b and the magnetic layers 2a and 2b since, as is clear from FIG. 15, the glass 3 is exposed in the recording medium sliding surface, and since the hardness of the glass 3 is lower than that of the non-magnetic bases 1a and 1b and the magnetic layers 2 and 2b compared with the non-magnetic bases 1a and 1b and the magnetic layers 2a and 2b. Thus, there is a possibility of the formation of step portions in the recording medium sliding surface, which would cause deteriorations in the performance of the magnetic recording medium.